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the membrane is so exceedingly delicate that it is scarcely possi- 
ble actually to.see it in either the young or in the old chloroplasts. 
But in those which are undergoing the act of bipartition, this sur- 
rounding membrane may at times be examined with some ease, 
although those fortunate times are not common. In such chro- 
matophores I have seen the membrane, but it becomes especially 
apparent in those which have been treated with alcohol to bleach 
the chlorophyll, followed by staining with eosin; fig. 2 represent- 
ing an optical section of a chlorophyll-grain after such treatment. 
_ The two grains are completely divided with the exception of the 
enveloping membrane which still binds them together. The 
alcohol has contracted the chromatophore, thus leaving the deli- 
cate membrane visible not only about and between the dividing 
planes, but around the margins of one of the chloroplasts, where 
it is, as usual, prevented from coming into contact with the body 
of the grain by the projecting ridges of the surface-structure. On 
the smaller chromatophore at the left-hand side the membrane is 
Not visible, but in the space separating the two grains it passes as 
a distinct but exceedingly delicate line, the space being bounded 
above, as shown in the figure, by a membrane conspicuously de- 
Pressed in the middle, the lower boundary being as plainly de- 
veloped. 
In fig. 4 is shown a greatly enlarged drawing of the inner 
ends of the same chloroplasts with the central membrane. The 
distance from one chlorophyll-grain to the other was about rsdo0 
inch. | have no means of measuring the thickness of the central 
membrane which separates the chloroplasts, but that membrane is 
double, This is an exceedingly “fine point” microscopically, and 
it is here that the « black-dot” resolution again makes itself useful. 
If the two membranes had been undivided or in actual contact 
throughout their whole length, the ‘double structure would of 
Course have been invisible. That they were not thus in actual 
contact the « black-dot” resolution demonstrates by exhibiting the : 
Minute black spaces near the upper and the lower extremities, as 
the chromatophores lie. horizontally across the field, the attempt 
to show this on the. greatly enlarged scale in fig. 4 being hardly 
More than a diagram. In fig. 2 the black, irregular line around 
the edge of one chromatophore represents the space between the 
Pn tas 
